An electric vehicle or a plug-in hybrid vehicle is equipped with an inverter for driving a motor coupled to wheels with the use of a high voltage battery, and a low voltage battery for activating accessories such as vehicle lights, and a radio.
On such a vehicle as above, a DC-DC converter that performs power conversion from a high voltage battery to a low voltage battery or from a low voltage battery to a high voltage battery is mounted.
It is desirable that such a vehicle as above should have the ratio of the space of the vehicle room to the entire volume of the vehicle as large as possible in order to secure riding comfort. It is required for the inverter and the DC-DC converter to be installed in small spaces other than the vehicle room such as an engine room.
Because the temperature environment of the engine room of this kind of vehicle is poorer than the use environment of a related vehicle, it is necessary for the inverter and DC-DC converter of this kind of vehicle to be cooled by a cooling device including a refrigerant formed of water and a mixture. Therefore, a cooling method and a cooling mechanism having high cooling efficiency and as small a footprint as possible become important technology components. One of these technology components is well known in which heats generated by switching elements of a DC-DC converter, a transformer, choke coils, bus bars, and the like are conducted to a cooling plate via solid conduction and radiated by the cooling plate.